This invention relates generally to a sealing mechanism and, more particularly to a heat sealing mechanism for use in a packaging machine for forming longitudinally spaced side seals in an elongated strip defined by two face-to-face panels of heat sealable film or web.
The strip usually is located in an upright plane and is intermittently advanced along a predetermined path. When the strip dwells between successive steps, heated sealing bars located on opposite sides of the strip are moved inwardly into engagement with the strip in order to seal the two panels of the strip to one another. The sealing bars then are retracted a short distance away from the strip before the next advance of the strip. Operation of the sealing bars is effected automatically at high speeds and in timed relation with the advance of the strip.
One type of well known side sealing mechanism includes pivotally mounted sealing bars which swing into and out of engagement with the strip. With a sealing mechanism of this type, provision is sometimes made for retracting the sealing bars to and holding the bars in a so-called "parked position" in which the bars are swung away from the strip by a significantly greater distance than is the case when the bars retract during normal operation of the machine. The bars are swung to the parked position automatically if an abnormal condition causes the machine to shut down. By parking the bars a significant distance from the stopped strip, the heat radiating from the bars will not soften or melt the strip.
In more advanced sealing mechanisms, the sealing bars are moved linearly into engagement with the strip. With linearly movable seal bars, the sealing pressure may be distributed more uniformly along the height of the strip and, in addition, the pressure may be more precisely controlled.